1. Field of the Invention
The present invention relates to a process for decontaminating soil and waste materials. More particularly, the present invention relates to a combination of processes including a thermal combustion process, a solvent wash process that utilizes carbon dioxide generated in the thermal process, and a vaporization process that utilizes heat energy generated in the thermal process, which in combination are used to remove volatile organic compounds from soil and other waste which have various levels of contamination.
2. Description of the Related Art
For many years a major problem occurring with the development of industry, in general, and the energy and petrochemical industry, in particular, has been the need to remove the oils and other hydrocarbons that have been spilled from the contaminated soil. The processes of choice have always been traditional thermal combustion processes, but the cost of these processes and the collateral damage that they can cause to the environment makes this solution unattractive in many cases. Most soil contamination is reported to be less than one percent (1%) by volume. The thermal processing of this material which contains very little hydrocarbon contamination is expensive at the very least, and most frequently causes damage to the soil. Further, the effects of the airborne contaminates and the use of ambient air in the thermal process can result in damage to a wide area.
Other treatment processes for contaminated soils lack the ability to clean or remediate the contamination. Burying soils in vaults has not been a viable or cost effective solution and the excavation and transportation of contaminated soil leaves the high possibility of scattering the pollution. The use of microorganisms or "microbes" has little value since much of the contamination either kills the organisms or they have little effect on the pollutant. Additionally, few people desire or will accept a sludge pit in their neighborhood.
With an increasing worldwide population and an increased per capita demand for energy, concern is now being raised over the environmental pollution resulting from the emission of gaseous byproducts from combustion processes. Even carbon dioxide, a gaseous compound produced during combustion by oxidation of carbon and which is essential to plant life is being viewed as a pollutant. Carbon dioxide has been identified as one of many "greenhouse" gases and its increased level in the earth's atmosphere is thought likely to contribute to an undesirable global warming effect.
A thermal process is taught by Wagner in U.S. Pat. No. 3,779,212 that a pure hydrocarbon fuel oxidized with pure oxygen produces carbon dioxide, water, and carbonic acid as products of combustion. Wagner further teaches that the carbonic acid rapidly disassociates into carbon dioxide and water resulting in only carbon dioxide and water as the ultimate products of the process. Wagner additionally teaches that the flame temperature associated with the combustion of pure methane with pure oxygen can reach 6,000 degrees Fahrenheit, (3,315.56 degrees Celsius). Wagner's invention is a specialized boiler designed to maximize thermal efficiency with very small size and low weight per unit of energy derived. For refractory lined combustion chambers and standard energy recovery boiler systems, lower combustion gas temperatures are required. Typical refractory limitations on continuous operating temperature are in the area of 2,500 degrees Fahrenheit (1371.1 degrees Celsius).
Additional background information can be found in U.S. Pat. Nos. 2,102,427 to Lloyd; 3,779,212 to Wagner; 5,309,850 to Downs; 5,179,903 to Abboud; 5,035,188 to Johnson; 4,860,670 to Jorgensen; 4,827,854 to Collette; 4,782,772 to Chughtai; 4,762,074 to Sorensen; 4,656,972 to Shimoda and 4,620,492 to Vogg. Additionally, Applicant's co-pending application Ser. No. 08/730,974 filed Oct. 16, 1996, now U.S. Pat. No. 5,906,816 provides additional background material.
It would be desirable to have a process that addresses and resolves most if not all of these concerns and interacts proactively to provide an acceptable, non-polluting, cost effective solution to this major social and environmental problem.